题目来源
Given a positive integer, return its corresponding column title as appear in an Excel sheet.

For example:

    1 -> A
    2 -> B
    3 -> C
    ...
    26 -> Z
    27 -> AA
    28 -> AB 

这个题目呢，一看呢，就感觉比较简单，感觉就是一个10进制转26进制的问题。代码如下：

class Solution {
public:
    string convertToTitle(int n) {
        string r;
        while (n != 0) {
            int x = (n-1) % 26;
            r += char(x+65);
            n = (n - 1) / 26;
        }
        reverse(r.begin(), r.end());
        return r;
    }
};